The invention thus starts out from a state of the art, as it is known from U.S. Pat. No. 2,942,389. In this method and apparatus, a bevel gear workpiece which is to be worked meshes rotatingly with a bevel-gearshaped tool having an abrasive surface thereon. The workpiece is thereby retarded, which allows the teeth of the tool to be guided so to speak, namely onto the workpiece tooth system. Understandably, this method does not lead to the desired success, because the workpiece tooth system is not without error. Thus, the tool tooth system follows so to speak the workpiece tooth system resulting in only a partial improvement and without completely overcoming the inexactnesses in the formed teeth.
Therefore, the basic purpose of the invention is to further develop the above-described method so that the work machining result is improved and the mentioned deficiencies are avoided. Furthermore, a suitable apparatus for carrying out the method is provided.
The aforementioned purpose is inventively attained by a method wherein backlash is provided in two places on two sets of gear pairs, namely, (1) between the successively engaging teeth on the workpiece and the tool and on one circumferentially facing side thereof remote from a first contact point and (2) between the successively engaging teeth on a pair of guide gears and on a side remote from a second contact point, which side faces in an opposite direction from the aforementioned one circumferentially facing side so that each set of gear pairs, namely, workpiece/tool and the two guide gears each have backlash but the four gears in combination are backlash free. The arrangement of guide gears on a workpiece spindle and on a tool spindle is actually known from German OS No. 33 04 980 (corresponding to U.S. application Ser. No. 816,946, filed on Jan. 6, 1986, which is a continuation of Ser. No. 576,672, filed on Feb. 3, 1984, now abandoned), where a method and an apparatus for the precision working of spur and helical gears is described. The use of guide gears in the precision working of bevel gears is, however, by all means not obvious, since the geometry of the bevel gears is a different one than the one of spur gears. This also results in different arrangements for the guide gears.
According to the inventive method, the tooth flanks of both straight and spirally toothed (or helically toothed) bevel gears can be precision worked. The preferred, however, not exclusive use lies in the working of hardened bevel gears, which heretofore could only be done using the slightly inexact lapping method or expensive precision grinding method.